The present invention relates to light-emitting materials, which can be deposited as a thin layer by vacuum deposition, and which can be used as effective dopants in organic light-emitting devices (OLEDs).
The progress of light-emitting diode (LED) over the past two decades has primarily focused on inorganic types because early development in organic light-emitting devices (OLEDs) resulted in poor fabrication and packaging, and short lifetimes. Today, gallium arsenide-based LEDs in the market are commonly available with efficiencies in some spectral regions exceeding conventional filtered fluorescent lamps. However, in the development of light-emitting materials for display technology, inorganic semi-conductor materials are not compatible for large-area assembled displays.
Pope et al. at New York University demonstrated organic electroluminescence in the 1960s based on anthracene materials (J. Chem. Phys. 38, 2042, (1963)). Much progress have been made since the discovery of the tris(8-hydroxyquinolato)aluminum (Alq3) based thin film device by C. W. Tang et al. at Kodak (Appl. Phys. Lett. 51, 913, (1987)). These contributed largely to the continuous discovery of new and improved electroluminescent materials. From small fluorescent molecules to conjugated polymers, many OLEDs have been shown to exhibit sufficient brightness, remarkable efficiencies, good operating lifetimes and desirable ranges of color emission.
Organic light-emitting devices containing metal complexes are of particular interest because of their unusual chemical and electronic properties. Some compounds bearing heavy metals exhibit potential advantages for OLEDs owing to their high internal quantum efficiencies. Conventionally, fluorescent materials are employed as dopants in emissive hosts. Singlet excitons (maximum theoretical internal quantum efficiency=25%) are formed after recombination of hole and electron to emit electroluminescence via dipole-dipole interaction through Forster mechanism (U.S. Pat. No. 6,310,360). Whereas, for heavy metal complexes, strong spin-orbit coupling can lead to singlet-triplet state mixing, which can result in high-efficiency electrophosphorescence in OLEDs (theoretical internal quantum efficiency up to 100%) (Nature, 395, 151, (1998); Synthetic Metals, 93, 245, (1998); Appl. Phys. Lett. 77, 904, (2000)).
However, some phosphorescent materials have intrinsic disadvantages, such as saturation of emission sites due to excessively long lifetimes as well as triplet-triplet annihilation and concentration quenching arising from strong intermolecular interactions at high doping levels (Phys. Rev. B. 60, 14422, (1999)).
For example, quadridentate azomethine-zinc complexes have been used as blue light emitters in organic light-emitting devices, which exhibit maximum luminance of approximately 1000 cd/m2 only (Jpn. J Appl. Phys., 32, L511 (1993); U.S. Pat. No. 5,432,014).
Azomethine-aluminum/gallium complexes have been employed in OLEDs as emissive materials. The current density of the device containing azomethine-gallium complex is 1 mA/cm2 at 10 V and the electroluminescence is greenish blue (U.S. Pat. No. 6,316,130).
It is therefore desirable to develop emissive dopant materials that can permit efficient energy transfer between the host and dopant in OLEDs, while causing little or no self-quenching even at sufficiently high doping concentrations.
Examples of objects of the present invention in embodiments thereof include:
The main objective of this invention is to prepare organic light-emitting devices (OLEDs) doped with new light-emitting materials. The devices exhibit low turn-on voltages and high luminance and efficiencies.
An object of the present invention is to provide thermally stable, moisture-resistant metal-chelated materials that can be deposited as a thin layer of known thickness by a vapor deposition process.
Further, the present invention concerns the design of high luminous dopants, which can be used at low concentration levels in light-emitting devices.
New light-emitting materials derived from quadridentate ONNO-type ligands, and a Group 10 metal (including platinum) were prepared as illustrated by formula I and II: 
wherein M represents Group 10 metal (including platinum) and R1-R14 are each independently selected from the group consisting of hydrogen; halogen; alkyl; substituted alkyl; aryl; substituted aryl, with substitutents selected from the group consisting of halogen, lower alkyl and recognized donor and acceptor groups.
Embodiments of the present invention includes, but is not limited to, OLEDs comprising heterostructures for producing electroluminescence which contain anode (ITO glass substance), hole transport layer (NPB(xcex1-naphthylphenylbiphenyl amine)), matrix emissive layer [host material (beryllium bis(2-(2xe2x80x2-hydroxyphenyl)pyridine) (Bepp2)) with different concentration of dopants as illustrated by formula I and II herein], charge transport layer (lithium fluoride) and cathode (aluminum metal).
The preferred embodiment as an effective dopant in the OLEDs herein is: 
The present invention provides new materials for applications as emissive dopants in electroluminescent devices. The invention includes the synthetic methods for these novel complexes plus their use as light-emitting materials. The devices of the present invention can be applied to field of display, light-emitter, display board for sign lamp, or light source for liquid crystal display.